Zika

Zika

Zika is a mosquito-borne virus primarily transmitted by Aedes aegypti mosquitoes1. It can also be transmitted sexually or through infusions of contaminated blood. Zika causes microcephaly, a serious brain defect that results in a baby’s head being smaller than normal. Zika may also lead to other brain and autoimmune problems, including Guillain-Barré syndrome (GBS).

Impact

Since 2015, 69 countries and territories have reported evidence of vector-borne Zika virus transmission . Local mosquito-borne transmission2 has been reported in the continental United States, and active Zika virus transmission is ongoing in South and Central America and much of the Caribbean . More than 2 billion people live in areas of the world where the presence of the Aedes mosquito and suitable climatic conditions could support local transmission of Zika4 .

Geography

Zika has been identified in more than 60 countries, and the outbreak is continuing to spread in many parts of the world.3,4.

Symptoms

Approximately 80% of people infected with Zika do not show any symptoms. Time from exposure to symptoms is likely a few days and symptoms usually last 2-7 days1. Symptoms are usually mild and include: 

  • Fever
  • Rash
  • Joint pain
  • Conjunctivitis (red eyes)

Other symptoms include: 

  • Muscle pain 
  • Headache

Zika can also be transmitted sexually, even if the infected person has no symptoms at the time; Zika can remain in semen longer than other bodily fluids5. Zika can also be transmitted through blood transfusion and in laboratory and healthcare settings.

A pregnant woman can pass Zika to her fetus during pregnancy5. Zika can lead to devastating consequences, including microcephaly, a serious brain defect that results in a baby’s head being smaller than normal, and can include problems such as eye defects, hearing loss and impaired growth. Zika also may lead to other brain and autoimmune problems, including Guillain-Barré syndrome (GBS), a disorder in which the immune system attacks nerves, leading to weakness and temporary paralysis. Zika virus infection in pregnancy appears to be the cause of a recognizable pattern of congenital anomalies that is consistent and unique6; Congenital Zika infection is being defined and described as cases occur7.

Long-term complications of Zika are unknown, testing for Zika is complicated and there is no vaccine or treatment so vector control is key to preventing vector-borne disease transmission.

History

The Zika virus was first discovered in a monkey in the Zika Forest of Uganda in 19478. Before 2007, 14 cases of Zika had been documented in humans, although other cases are likely to have occurred and were not reported. Zika outbreaks occurred in areas of Africa, Southeast Asia, and the Pacific Islands before 20158. Many cases may not have been recognized, because the symptoms of Zika are similar to those of many other diseases.

On May 7, 2015, the Pan American Health Organization (PAHO) issued an alert regarding the first confirmed Zika case in Brazil9. In October 2015 Brazil reported an association between Zika virus infection and microcephaly. On February 1 2016, WHO declared Zika a public health emergency of international concern, defined as "an extraordinary event which is determined to constitute a public health risk to other States through the international spread of disease and to potentially require a coordinated international response”.

Prevention

Prevention is key, and the best line of defense against Zika is to avoid being bitten by mosquitoes that may carry the virus. Zika is transmitted by Aedes aegypti, a black and white mosquito that bites during the daytime. Flight range studies suggest that most female Ae. aegypti may spend their lifetime in or around the houses where they emerge as adults and they usually fly an average of 400 metres. This means that people, rather than mosquitoes, rapidly move the viruses they carry (dengue, Zika, chikungunya) within and between communities and places10. The immature stages are found in water-filled habitats, mostly in artificial containers closely associated with human dwellings and often indoors10. The following measures can be used to prevent mosquito bites outdoors and during the daytime:

  • Use an insect repellent on exposed skin
  • Mosquito-proof homes: install or repair screens on windows, doors and porches
  • Remove standing water in and around homes 
  • Wear light colored clothing, long-sleeved shirts and long pants 
  • Cover children’s crib, stroller and baby carrier with mosquito netting
  • Anyone infected with Zika should sleep under a mosquito net to prevent further transmission
  • Expectant mothers should avoid travel to Zika-affected areas and If infected with Zika, couples should avoid sex or have protected sex

1www.who.int/mediacentre/factsheets/zika/en/

2www.who.int/emergencies/zika-virus/en

3For the latest updates and travel warnings see: www.cdc.gov/zika/geo/index.html

4Messina, J., Kraemer, M. et al. (2016) Mapping global environmental suitability for Zika virus. eLife Digest, 5 (www.elifesciences.org/content/5/e15272).

5www.cdc.gov/zika/transmission/index.html

6http://www.medscape.com/viewarticle/871391

7www.who.int/bulletin/volumes/94/6/16-176990/en/

8 Centers for Disease Control and Prevention, “Zika Overview.” Accessed Nov. 11, 2016. Available at: www.cdc.gov/zika/about/overview.html

9 Centers for Disease Control and Prevention, “Key Messages- Zika Virus Disease.” Accessed Nov. 12, 2016. Available at: www.cdc.gov/zika/pdfs/zika-key-messages.pdf

10 www.who.int/denguecontrol/mosquito/en/

 

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